This invention relates to a method of forming a fluorescent screen for color picture tubes.
The fluorescent screen for a color picture tube comprising picture elements of triads of green, blue and red phosphors arranged in a regular pattern is generally manufactured by utilizing photo-chemical reactions as well known in the art.
One of such methods is a so-called dry process in which a film of a photosticky substance which becomes sticky when exposed to light is issued and phosphors are adhered to this film. This invention relates, more particularly, to the improvement of such a dry process.
The aforementioned dry process will now be described specifically below.
A substance which becomes sticky when exposed to light is coated on a panel inner face of a bulb. Used as such a substance is a composition mainly containing diazonium compound, i.e. complex salt of a diazonium compound with halogenized metal salt (zinc chloride, cadmium chloride, stannous chloride) or with non-metal fluoride salt fluoroboric acid etc.) including polymer compounds, and surfactants as additives. Such substances are thought to become sticky because diazonium compound frees deliquescent substances when it is decomposed by exposure to light.
Next, a color selection electrode such as a shadow mask is mounted on the panel through which portions, where the phosphor emitting the first color, for instance, green, are to be applied, are exposed to light. The portion which has been exposed to the light which passes through apertures in the shadow mask exhibits sticky properties. Then, the powder of phosphor of the first color is applied on the inner face of the panel to be sufficiently adhered to the portion which has become sticky. Surplus powder on unexposed portions is then removed by development such as air blowing. Now the panel inner face has been provided with picture elements of the first color phosphor. The aforementioned steps following the exposure step will be repeated consecutively for other two colors to complete picture elements of phosphors of three colors, i.e. green, blue and red.
In the prior art process described above, following the formation of phosphor picture elements of three colors, in advance of subsequent filming or aluminizing, it is required to wash the panel inner face with water or the like to sufficiently remove the residue of diazonium compound. This is necessary because the brightness of the fluorescent screen is reduced by the residue of diazonium compound if remained thereon. With the conventional process, however, it is difficult to obtain a fluorescent screen of high quality during washing since the adhesiveness thereof is weak.